Variable speed starter for X-ray tubes

ABSTRACT

A solid state starter to selectively accelerate X-ray tube rotors to the low speed utilized for fluoroscopic examinations and up to the high speed required for spot-film or radiographic exposure operation, and wherein the speeds of the rotor may be varied throughout the speed range.

BACKGROUND OF THE INVENTION

The present invention relates to U.S. Pat. No. 3,641,408 and to thecorresponding Reissue Patent No. 28,618 entitled "SOLID-STATE POWERSUPPLY SYSTEM FOR ROTATING ANODE X-RAY TUBES," issued to Louis L. Fioccaand assigned to the same assignee as the present invention. Louis L.Fiocca, the inventor of the system of Reissue Patent No. 26,618 is alsothe inventor of the present invention and Mr. Fiocca's continuing workwith the system disclosed in the Reissue Patent No. 28,618 resulted inthe improvement comprising the present invention.

As will be appreciated, the present invention utilizes a similarconcept, and much of the circuitry disclosed is the system of theReissue Patent No. 28,618 and, in fact, the present invention eliminatesa significant portion of the circuitry of the system disclosed in theReissue Patent No. 28,618 while providing an improved operating result.Accordingly, for the purpose of simplification of the description of thecircuitry in this application, reference as appropriate is made to saidReissue Patent No. 28,618 for the details of the circuitry shown anddescribed therein.

X-ray tubes having rotatable anodes are well known. In such tubes, theanode is caused to rotate to present a continually changing target areaso that heat generated by the X-ray bombardment may be more easilydissipated. This heat dissipation enables higher energy levels to beused resulting in increased X-ray output as compared with tubes havingfixed anodes.

The rotating anodes of X-ray tubes are generally driven with split phasemotors and in fact may be the rotors of said motors. The motors havebeen heretofore operated from power sources capable of providing either60 Hz or 180 Hz A.C. control power to enable anode rotation at a firstrelatively low speed and at a second relatively high speed. Such priorart systems require means to accelerate from a quiescent condition toattain the final operating speed for the X-ray anode in the desiredoperating running mode.

The rotating anode and the motor drive generally exhibit mechanicalresonances at the speed in the range of 4,000 to 6,000 and RPM and it isdesirable to make the transistion through such resonances both onacceleration and deceleration of the anode as briefly as possible tominimize bearing wear of the anode system and to minimize undue strainon the bearing mounts and the tube structure.

In the prior art, X-ray tube starter systems, such as shown in theReissue Patent No. 28,618, a first starter or drive system has beenutilized to drive the rotor up to its slow speed operating condition anda second starter has been utilized to drive the rotor to its high speedoperating condition. Two essentially separate starting systems areemployed, and the systems operate in generally digital or discretefashion.

In contrast to the prior art, the present starter and drive systemoperate in an analog manner and can be controlled to accelerate or boostthe rotor to a first selected running speed, and can also be controlledto accelerate and boost the rotor to a second selected running speed,and either of the selected running speeds can be varied within a givenoperating range.

The well known principle of phase control of SCR's (silicon controlledrectifiers) described and utilized in Reissue Patent No. 28,618 is alsoutilized and applied in the present invention.

Briefly, and as is well known, an SCR which is gated or triggered toconduction, will conduct for the remainder of a half cycle of the A.C.(alternating current) wave provided to its anode - cathode current path.Thus, dependent on the point at which the SCR is triggered toconduction, relative to the phase angle of the applied A.C. wave, theSCR will conduct current for a selected controllable time period.

Consider briefly an application of the present invention. An X-rayexamination will conventionally have at least two X-ray tubes; one ofthe tubes is normally for doing fluoroscopic examinations and isreferred to as "undertable tube," and the other tube is normally usedfor doing radiographic exposures and is commonly referred to as the"overtable tube". For doing fluoroscopic examinations, the undertabletube is operated at a relatively low speed such as at 100 RPM andtherefore, this tube requires a low speed starter to boost the rotatingspeed of the rotor to a desired relatively low rotating speed. Incontrast, radiographic exposures are preferably done at high speeds, sayat 10,000 RPM, and therefore the overtable tube requires a high speedstarter to boost rotating speed of the rotor to a relatively highrunning speed. The present invention provides a single starter and drivemeans for accelerating and operating both of the aforesaid tubes at therequired operating speeds.

As discussed above, the circuitry in the present application is similarto that of the Reissue Patent No. 28,618 with the improvement that the60 Hz phase shift network block 20, the 60 Hz SCR bridge 21 and the 24VDC logic power supply 11 coupled to block 20, and the two second timer26 are removed from the system of the present invention. In addition toeliminating components and circuitry and reducing costs, the presentcircuitry provides improved operating results over the circuit disclosedin U.S. Pat. No. 3,641,408, as will be explained.

As also mentioned hereinabove, since the circuitry of the presentinvention is in considerable part the same as that described in theReissue Patent No. 28,618, reference is specifically made to that patentas needed to clarify the description of the present invention. And thereference numerals referring to the blocks in the FIGURE of the presentinvention refer to the similarly numbered blocks in FIG. 1 of theReissue Patent No. 28,618.

DESCRIPTION OF THE SOLE FIGURE

The sole FIGURE of the invention is a block diagram of a solid-statepower supply system, which embodies the present invention for the drivemotor of a rotating anode X-ray tube.

DESCRIPTION OF THE INVENTION

Refer now to the sole FIGURE which shows the system 12 of the presentinvention. In operation, a 240 volt A.C. 60 Hz input voltage applied toa control transformer 10 supplies a 24 volt D.C. power supply and a 180Hz phase shift network 16 with appropriate input voltages. As mentionedabove, the blocks of system 12 have been described in detail in ReissuePatent No. 28,618, and need no further description herein.

Power supply 11 generates D.C. output voltage of approximately 24 voltswhich are employed to supply a 180 Hz oscillator amplifier 14.Oscillator amplifier 14 develops a 180 Hz output signal which issupplied through an inverter driver 15 to SCR inverter 18 to develop a180 Hz square wave output signal. A sinusoidal filter 23 derives thefundamental component of the square wave output from SCR inverter 18 todeliver 180 Hz sine wave signal to selection relay contactor 22, andthen through rotor relays and split phase capacitor network 24 to thestator terminals of the drive motor for the X-ray anode tube to therebyprovide the motor with a high speed synchronous driving power.

The selection relay contactor 22 also receives an input from full waveD.C. brake and timer 30 which provides a selective 5 second D.C. signalcomprising a rectifier pulsating A.C. signal to provide a braking actionto the anode rotor.

The remaining portion of the circuit to be described provides a meansfor controllably operating the motor at a selected accelerating orboosted voltage condition, at the selected running speed or formaintaining the motor at its quiescent condition. The programming inputrelay logic 27 controls the amount of phase shift provided by a phaseshift network 16. Phase shift network 16 develops a signal whichcontrols the amplitude of the output signals from the A.C. to D.C.Conversion unit 17 which comprises a full wave bridge circuit, and thesignal to determine the operating mode of the motor, as will beexplained.

The A.C. to D.C. Conversion unit 17 provides a D.C. driving signal whichis coupled to the SCR inverter 18. As also described in the ReissuePatent No. 28,618, dependent on the programmed input signal, for theprogramming input relay logic 27, the output provided by Conversion unit17 can be 0° to 180° out of phase with the input to the A.C. to D.C.Conversion unit 17 from the 240 VAC 60 Hz input.

When 0°phase shift provided by phase shift network 16 is 0°, the firingangles of the A.C. to D.C. Conversion unit, or full wave SCR bridgecircuit 17, is such as to allow nearly 180° of conduction of each of theSCR's. This is the boosted condition and will allow maximum current flowin the full wave bridge circuit 17. The output from the SCR bridgecircuit 17 charges associated output capacitors and the charge on thecapacitors provides an increased D.C. voltage which increased or boostedvoltage constitutes the supply voltage for the 180 Hz inverter 18. Theinverter 18 is a free running inverter commutated by a capacitor in aconventional McMurray Bedford which drives the primary winding of atransformer whose output in turn powers the anode motor.

In the run condition of the motor, a phase shift is provided to the SCRConversion unit 17 such that the firing angle of the SCR's is less than0°. Accordingly, the charge on the associated capacitors is a reducedD.C. voltage and the inverter 18 operates at this reduced voltage level.

The phase shifted signal provided by the network 16, thus controls theoutput from SCR bridge circuit 17 and thus SCR bridge circuit 17 can becontrolled to provide an added voltage or drive to the inverter circuit18 to vary the drive to the anode motor from a maximum acceleration to aminimum acceleration or run condition in an analog or smooth mannerdependent on the input from the programming input relay logic 27.

The inventive system 12 can thus be connected or switched to provide aboost voltage to a selected X-ray anode rotor. The boost voltage can beutilized to provide a required acceleration to an anode rotor and/or adesired increase in the anode rotor running speed.

The one second timer 25 is coupled to phase shift network 16, andprovides means for automatically timing the time period of the boostmode of operation. The timing sequence or period of the timer 25 isinitiated by the programming input relay logic 27.

The full wave D.C. brake and timer provides a 5 second braking signalprogrammed by the programming input logic 27 to provide the braking tothe anode rotor. The braking signal comprises, in effect, a full waverectified A.C. signal.

While the invention has been particularly shown and described withreference to a preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the spirit and scope of theinvention.

What is claimed is:
 1. A system operable from an alternating currentsource, for controllably providing power to an induction motor fordriving rotating anodes of X-ray tubes, said motor being operable toselectively drive the anode within a given speed range at a first lowrate of speed and at a second higher rate of speed, a drive controlcircuitry for controlling the operation of the motor at the low speedoperation and said same drive control circuitry controlling theoperation of the motor at the higher speed operation, analog operatingmeans for said control circuitry for providing voltages at selectedfirst levels to the motor to thereby accelerate the anode to theselected speed within the given range, and said analog operating meansproviding voltages at selected second levels to the motor to maintainthe anode rotating at the selected speed.
 2. A system as in claim 1comprising means for multiplying the frequency of the alternatingcurrent, an inverter for receiving the current at the multipliedfrequency and providing driving power to said motor, a phase shiftnetwork for receiving the alternating current and shifting the phasethereof, programming means for determining the amount of phase shiftprovided by said phase shifting network, SCR bridge means for convertingalternating current to direct current and coupling said direct currentto said inverter, means coupling said phase shifted current from saidphase shift network to said SCR bridge, and the output from said SCRbridge being dependent on said phase shift network, and the output fromsaid SCR bridge to said inverter determining the drivng power coupledfrom said inverter to said motor to thereby control in an analog mannerthe acceleration of said motor and also its speed of rotation.
 3. Asystem as in claim 2 further including means for timing the length ofthe period said phase shifting network provides an output to said SCRbridge and the time said SCR bridge provides a maximum output.
 4. Asystem as in claim 2 wherein the programming means determines the firingangle of said SCR bridge and the output of said SCR bridge determinesthe power output from said inverter.